Continuously adjustable speed electric drive



Dec. 14, 1948. P. J. MCLAREN- ETAL 2,456,522

CONTINUOUSLY ADJUSTABLE SPEED ELECTRIC DRIVE 7 Sheets-Sheet 1 Original Filed Jan. 28, 1943 fh eir A Horn evs Dec. 14, 1948. H J, CL N ET AL 2,456,522

CONTINUOUSLY ADJUSTABLE SPEED ELECTRIC DRIVE Original Filed Jan. 28, 1943 7 Sheets-Sheet 2 i v z iheir Ailorneys 1943- P. J. M LAREN ETAL 2,456,522

I CONTINUOUSLY ADJUSTABLE SPEED ELECTRIC DRIVE 7 Original Filed Jan. 28, 1943 7 Sheets-Sheet 3 4 fNvExvTogs BY Mace/v Fey 7 iheir'Allorneys Dec. 14, 1948. P. J. MQLAREN ETAL 2,456,522

CONTINUOUSLY ADJUSIABLE SPEED ELECTRIC DRIVE Original Filed Jan. 28. 1945 4 7 Sheets-Sheet 5 their Aifornys Patented Dec. 14, 1948 UNITED STATES PATENT OFFICE CONTINUOUSLY ADJUSTABLE SPEED ELECTRIC DRIVE Continuation of application Serial No. 473,800,

January 28, 1943.

5 Claims.

1 p This invention relates to driving mechanism, constantly under the control of an operator, for producing at will any desired output speed be- This application May 18, 1948, Serial No. 27,807

site directions throughout a wide range of adtween positive limits and between negative limits,

and more particularly to a combination of a plurality of such reversible, variable speed, driving mechanisms under the influence of a common control member which is operable, independently but simultaneously and coordinately, to vary and control the directions and speeds of outputs o the respective driving mechanisms.

Although the invention is by no means limited in its application to the aiming of guns, it has particular utility in that field and may be most conveniently and advantageously disclosed in connection with gun aiming means.

In the illustrative embodiment of the present invention a gun turret, mounted for rotation, supports one or more guns for rotation in unison with itself and also with capacity for rotation about an axis at right-angles to the turret axis. The gun or guns are thus caused to be operated in azimuth by rotation of the turret and are caused to be operated in elevation by rotation relative to the turret. A control member, displaceable in either of two opposite directions'from an azimuth neutral attitude, determine the direction of operation in azimuth by the direction of its displacement, and the speed of operation in azimuth by the extent of such displacement.

The same control member is also displaceable in either 'oftwo opposite directions from an elevation neutral attitude and determines the direction of operation in elevation by the direction of its displacement, and the speed of operation in elevation by the extent of such displacement.-

Dperations in azimuth and in elevation may be concurrently, independently controlled; and hence the operator has it in his power to eflfect operation of the gun or guns in any desired direction and at any desired speed within limits.

It is an important object of the present invention to provide azimuth and elevation electric drives in combination with one another and with common control means of the character indicated above.

In a broader aspect, it is a salient object of the invention to provide eflicient and dependable driving mechanism for producing with accuracy any selected output speed in either of two oppo-.

justment.

It is a further object to provide an uninterruptedly adjustable, variable speed driving mechanism of the kind referred to, adapted for regulation by a manual or mechanical control member, and of such nature that the output speed may be a definite function of the direction and extent of displacement of the control member from a neutral or datum position. In other words, the

output speed is so definitely related to the position of the manual control member that the manual control-membercan be utilized as an accurate speed indicator and guide, and/ or as a means afor running a measure of speed into apparatus whose operation requires an accurate measure of the speed for an input.

It is a further object of the invention to provide an electric drive of the kind referred to, thereby eliminating the Variables and uncertainties which are inherent in hydraulic drives and in mechanical friction drives, while avoiding such important drawbacks as the fine manufacturing requirements of the former, and the excessive wear of the latter.

. It is a further object of the invention to provide an electric drive in which speed responsive means, driven by a motor, is operative upon a driving circuit or circuits of the motor constructed and arranged to cause the output speed to be reduced when the output speed exceeds the speed characteristic of the position of the control member, and to cause the output speed to be increased when the output speed has been reduced below the speed characteristic of the position of the control member.

It is a further object of the invention to provide, in combination with an electric motor, make andbreakmechanism responsive to the speed of the motor and settable by a control member to interrupt and reestablish field current supply at any selected speed within the positive and negative operative ranges, together with means automatically adjustable in response to operation of the control member to limit current flow through the armature to safe values under all operating conditions.

Important features of the invention have to do with means for making practical and effective direct current electric drives of the kind referred to, and means for making practical and effective alternating current drives of the kind referred to.

Advantages of the present invention reside in the fact that the control has virtually no load lag, and i inherently stable. Further advantage is present in that the controlling elements of the regulator may be placed at a point remote from the controlled elements.

The present application is a continuation of the pending application of Peter J. McLaren, John A. Vaughan and Macon Fry, Serial No. 473,800 filed January 28, 1943, now abandoned.

Other objects and advantages. will hereinafter" appear.

In the drawing forming part of thisspecification Fig. 1 is a fragmentary perspective view 0121 turret and gun assembly in which the' invention is embodied;

Fig. 2 a fragmentary perspective view illustrating important elements of the control mechanism of Fig. 1;

Fig. 3 is a diagrammatic view illustratingcom trol circuits of a single one of the electric drive units as employed in the apparatus of Figs. 1 and 2, the electric drive being organizedfor direct current operation;

Fig. 4 is a diagrammatic view illustrating a second form of electric drive adapted for D. C. operation;

Fig. 5 is a sectional view, largely diagrammatic; of a third form of electric drive adapted for D. C. operation;

Fig. 6 is a diagrammatic view illustrating a fourth form of electric drive adapted for A. C. operation;

Fig. 7 is a diagrammatic view illustrating a further form of electric drive adapted for A. C. or D. C. operation;

Fig. 8 is a graph illustrating certain operating characteristics of the electric drive of Fig. 4;

Fig. 9 is a vector diagram illustrating and explaining principles and relationships applicable to Fig. 6; and

Fig. 10 is a diagrammatic view illustrating a further form of electric drive adapted forD. C. operation.

In the embodiment of the invention disclosed in Figs. 1 to 3, each of the drives, azimuth and elevation, comprises a direct current motor I as diagrammatically shown in Fig. 3. The motor is shown as energized from a D. C. source through line conductors 2 and 3. The motor is of the double shunt type, having opposed field windings 4 and 5. ture from line conductor 2 through a closed ring resister 6, which will be referred to in greater detail hereinafter, and a conductor 1, and is re-' turned to line conductor 3 through a conductor 8. A suitable line switch (not shown) may be that their operating characteristics will not be substantially altered by change of tempfirature Current is supplied to the motor arrnawhen the moi-or is set into operation. In the neutral condition, as illustrated in Fig. 3, the ring resistor 6 interposes a high resistance in series with the armature and protects the motor against damaging overload.

The motor is set into operation in'one direction or the other by short circuiting one or the other of the field windings 4 and 5, and provision is made of speed responsive mechanism operated by the motor for interrupting the short circuit at any selected speed in either direction.

For this purpose a conductor l3 runs from conductor H) to a contact arm M. The arm l4 includes a contact l5 which is adapted to be moved into enga ement with a stationary contact I6 and thus, through a conductor I! connected to the contact I6 and to the conductor 9, to complete a short circuit path around the winding 5. The contact arm is also includes a contact is which is adapted to be moved into engagement with a contact I9 and thus, through a conductor 20 which is connected to the contact l9 and to the conductor ll, to complete a short circuit path around the field winding}.

The short circuit paths are closed alternatively. When the windingl is short circuited the winding 5 is effective to produce rotation of the motor shaft l2 in one direction, and when the winding 5 is short circuited the winding 4 is effective to produce rotation of the motor shaft l2 in the other direction.

The contact arm I4 is manually operable by a control slide 2| having a control handle 22. The slide 2| in thepurely diagrammatic illustration of Fig. 3is shown as formed with slots 23 and is slidably mounted upon stationary headed studs 24. In the actual. physical structure illustrated in Fig. 2 the members corresponding to the slide 2| are rotary members and there are other minor physical differences, but the principle of operation is that illustrated in Fig. 3. Motion of the slide 2| is yieldingly transmitted to the contact arm l4 through opposed tension springs 25 and 26. The spring 25 is anchored at its left-hand endto the slide 2| and atits right-hand end to a head member 21 of the contact arm M. The spring 26 is anchored at its left-hand end to the head member 2Tof the contact arm l4 and at its right-hand end to the slide 2|.

When the slide 2| is moved toward the left from the neutral position illustrated in Fig. 1, the arm I 4 is carried toward the left until arrested by engagement with the contact I6. Further movement of the slide 2| toward the left places the spring 25under progressively increasing tension. Similarly, when the slide is mov toward the right from the'neutral position 01 Fig. 1, the contact arm I! is moved toward the right until arrested by engagement of contact |B with contact 19. Further movement of the slide 2| toward the right places the spring 26 under progressively increasing tension. In either case the movable contact is held' yieldingly against the stationary contact with a force-whose magnitude dependsupon' the position to which the slide 2| has been moved.

As soon as contact I5 is closed onto contact |6 by movement of the slide'toward the left. the winding 5 is shorted out and the winding 4 becomes fully effective to drive the motor shaft in a definite direction. Similarly, as soon as the contact H3 is closed on contact IS the winding 4 is shorted out and'the winding 5 becomes fully effective to drive the motor shaft in the opposite d rect on.

Provision is made in either case for limiting the speed of themotor to a speed characteristic of the position to which the slide has been moved by the handle 22. It is characteristic of a properly designed motor generator to produce a voltage output which bears a definite relationship to the speed of the motor. If, therefore, the motor is caused to drive a generator, and a device capable of accurately responding to the generated voltage is utilized to regulate a control, the system may be employed to govern the speed of the power motor driving the generator.

A direct current generator 28, driven by the motor l, is connected to a galvanometer29. The circuit is established through conductors 30, 3|, 32, a slide contact 31 carried by the slide bar2l, a resistor 33 and a conductor 34. The resistor 33 will be explained in further detail hereinafter. The contact arm [4 is fixed on shaft 35 of galvanometer 29, and hence has appliedto it a torque depending for its direction upon the direction of rotation of the motor generator, and for its magnitude upon the voltage generated by the generator. This galvanometer torque is applied in the direction to move contact I5'away from contact it against the tension of spring 25 when rotation of the motor has been brought about by closing ,of the contact 15 on the contact. I 6, and is in the direction to move contact 18 away from contact l9 against the tension of the spring 26 when the operation of the motor has been brought about by closing of the contact l8 on the contact 19.

Since the principle of operation is the same in either case an explanation for one case will suffice for both.

When the control handle 22 has been moved to the right, closing contact l8 upon contact I9, and then putting a further predetermined tension upon the spring 26 according to the distance that the slide is moved to the right, engagement of the contacts [8 and [9 will be maintained until the motor has attained a speed characteristic of the position in which the handle 22 is held. As the motor gains speed an increasing counterclockwise torque is ap-plied to the contact arm I 4, and when this torque is sufficient to overcome the tension of spring 26, thearm I4 is moved to the left to break engagement of the contact 18 with'the contact l9. This brings about an immediate slowing down of the motor I. The slow ing down of the motor reduces the voltage generated by generator 28 and reduces the torque applied by galvanometer 29 to arm I4, so that the torque is no longer able to overcome the tension of the spring 26 and the spring returns the contact l8 to engagement with contact l9, thereby again increasing the speed of the motor. Engagement is broken and reestablished in rapid alternation, the departures from the desired average speed being very slight. 1

When the line switch is closed and the motor is not running, the current flow through the armature is limited only by the resistance of the conductive path through the armature, includingthe ring resistor 6, and hence the resistor 6 is constructed and arranged to interpose a high resistance in the neutral condition of the parts. As the motor acquires speed in either direction, however, a counter E. M. F. is developed and the eifective resistance of resistor 6 can be, and is, reduced, without liability of destructive current flow through the armature, and with the advantage that more output power can be developed with the same motor and with the same, expendifecting the speed responsive means. The motor speed formula is V- I,,R,, E,

where n is motor speed in revolutions per second, V is the voltage between the supply mains, Ra, is the resistance of the armature circuit, Ia is the current flowing through the armature, is the armature flux, K is a constant, and E5. is the counter-electromotive force.

The lesser speed n at which the speed responsive mechanism acts for any given setting of the handle 22 to interrupt acceleration of the motor toward the speed 11 depends upon the torque applied by the spring 25, 26 at that setting being overcome by the opposing torque developed by the galvanometer when the motor has attained the speed n. The torque applied by the spring 25, 26 for a given setting of the slide 22 depends upon the length and stiffness of the spring, and may therefore be predetermined by proper selection of the spring. The stress of the spring employed is a linear function of the displacement of the handle 22 from the neutral position. The opposing torque developed by the galvanometer at speed ndepends upon thegalvanometer characteristics, the generator characteristics, and the value of any resistance which may be interposed in the generator-galvanometer circuit.

By utilizing a variable resistance 33 in the genorator-galvanometer circuit and controlling 33 from the handle 22, the galvanometer torque may be made to bear a non-linear relation to the speed of the motor-generator, and thereby to bring about a non-linear relation between the displacement of the handle 22 and the resulting increment of the speed 11/ at which the speed responsive means will cause the arm M to break contact. This is desirable in order that a finer and more sensitive speed control may be realized in the low speed range than in the higher speed range. The non-linear relationship can be accentuated, or adjusted as desired, by making the resistance33, itself, non-linear in its response to movement of the handle 22. The resistance 33, for example, may be a winding made up of short turns at the middle and progressively longer turns toward the ends, so that the slide contact 31, as it moves outward from the neutral position, cuts in a greater increment of resistance for each uniform increment of movement. Whatever law of variation is selected for displacement of the handle to one side of the neutral position will desirably be, selected also for displacement of the handle to the other side of the neutral position.

Since movement of the handle away from neutral to any setting tends to accelerate the motor at least to a speed 11. characteristic of the motor for that setting under full load conditions, which is greater than the speed n for which the speed responsive mechanism is correspondingly set by the same movement of the handle, the circuit breaking operation of arm |4 atspeed n by the speed responsive means always acts to interrupt motor circuit conditions' whichlare acting to produce acceleration, and to reestablish the'original balanced or neutral circuit conditions which tend to produce and maintain a state of rest. The motor, therefore, is caused to slow down to the slight extent necessary to reestablish the :drive, and thus the motor speed is held to the desired average speed n with very slight and very rapid fluctuations above'and below that speed.

If for any reason the motor should tend to speed up when it should slow down after'a circuit breaking operation of arm l4, arm M will be quickly moved over to close the opposite pair of contacts and will be caused thereby to establish momentarily the reverse driving condition, thus assuring a prompt slowing down. This is true in all the forms of the invention illustrated herein.

In providing for a reduction in value of the effective resistance of the resistor 6 as'the control handle 22 is moved in a direction to increase the speed setting n of the speed responsive means, it is important that the resistance be maintained nevertheless at such value for each speed n that no destructive increase of current flow through the armature shall occur.

We have found that if, for each speed setting 11' of the speed responsive means, the resistor 6 is adjusted to a resistance value such that IaRa be greater than V/2 at the motor speed for which the speed responsive means is set.

A slide contact 36 connected to the conductor 2 and carried by the slide 2| engages the ring resistor 6 and is shifted relative to the resistor by and with the slide 2|. As shown in Fig. l the parts are in neutral and the slide'36 engages the center point of the resistor 6. This provides equal parallel paths to the conductor 1, and interposes the maximum resistance between the conductor 2 and the conductor 1. When the slide contact 36 is moved toward the right from the center positon the resistance is progressively diminished, and when the slide contact 36 is moved toward the left from the center position the resistance is also progressively diminished.

The resistor 8 is desirably non-linear in its construction. It may, for example, take the form of a winding having relatively long turns at the middle and progressively shorter turns outward from the middle.

Two drivin units like that diagrammatically illustrated in Fig. 3 are employed in the mechanism of Figs. 1 and 2, one for driving a turret about a vertical axis, and the other for driving a gun support about a horizontal axis which is fixed relative to the turret. The rotation of the turret operates the guns in azimuth, While rotationoi' a horizontal shaft upon which the guns are mounted operates the guns in elevation. All of the mechanism illustrated in Figs. 1 and 2, with the exception of a stationary internal gear 4|, is mounted upon the turret and participates in the movement of the turret about the vertical axis thereof. A stationary casing 42 comprising lower and upper casing members 43 and 44 is afiixed to the turret and supports a control box 45.

The control box 45 is mounted on the casing 42 for rotary movement about the axis of a statlonary vertical shaft 46. A sleeve 41 extends through the opposite side walls of the control box 45, being mounted in the walls with capacity for rocking movement abouta horizontal axis. Handle members 48 are affixed to the opposite protruding ends of the sleeve 41. The sleeve 41 together with the handles 48 constitute a common control member for both the azimuth and'elevation drives.

.A gear segment 49 within the box has a hub portion 50 thereof aflixed, as by means of a set screw 5|, to the sleeve 41. Control of the elevation drive is effected through rotation of the gear segment 49 in unison with the sleeve 41.

'As illustrated, the parts are in the elevation neutral position, being biased toward and yieldin'gly retained in thisposition by means of a coil spring 350. As best seen in Fig. 2, the springSIfl extends around a hub portion of the segment 48 within the box 45, and has its opposite ends turned upward to form arms5| and 52 which lie normally at opposite sides of a pair of fixed pins 53. The pins 53 are mounted on a side wall of the box 45 to extend inwardfrom said wall. A pin 54 carried by the gear segment 49 extends outward between thearms' 5| and 52.

Clockwise rotation of the sleeve 41 from the position illustrated in Fig. 2 causes the pin 54 to push the arm 5| around in a clockwise direction while corresponding movement of the arm 52 is prevented by the pins 53. Such movement, therefore, causes contraction of the spring 50 and places it under a progressively increased stress, so that the spring tends through the arm 5| to return the sleeve 41 and the control handles 48 to the initial position as illustrated. Similarly, when the control member is operated in a counter-clockwise direction away from neutral, the arm 52 is moved in a counter-clockwise direction while the arm 5| is restrained by the pins 53. The spring, acting through the arm 52, tends therefore to return the parts in a clockwise direction to the condition illustrated in Fig. 2. The spring may be constructed and arranged to be under any predetermined stress when the parts are in neutral position, and hence may be caused to exert any neutralizing force desired.

The gear segment 49 is connected through a pin 55, carried by the gear segment, and a link 56, to azpin 51 carried by crank 58 fast on vertical shaft 59. The shaft59 has affixed to it a gear segment 60 which meshes with a pinion 5| fast on a vertical shaft 62, A collar 63 on the shaft 62 is connected through a coil spring 25c with a contact arm Me which is fast upon a vertical shaft 35c of a galvanometer 29c. Contact blades |5e and |8e carried by the block |4e extend between the arms of a stationary contact carrying block 64. The block 64 is fixed upon a horizontal partition wall 65 of the box 45. The block 64 carries a pair of contacts corresponding to the contacts l6 and IQ of Fig. 3.

The spring 25s. is under no initial stress. When the shaft 52 is turned away from neutral in either direction, the block |4e..and the shaft 35c turn in unison with it until arrested by one or the other of the contacts carn'ed by the block 64, dependin upon the direction of rotation. In one direction continued rotation of the shaft 62 after the block Me has been arrested puts the spring 25c under stress by forcing the spring to expand, while in the'opposite direction continued rotation of the shaft62 after the block Me has been arrested puts the spring under stress by forcing the spring to contract. The spring 25c, therefore, serves the combined function of the springs 25 and 26 dia- 9 grammatically illustrated as the equivalent of spring 25e, in Fig. 3.

The gear segment 49 meshes with a pinion 66 which is fast upon a horizontal shaft 61. The shaft 61 extends through a stationary casing 68 within which there is supported a resistor 33c corresponding to the resistor 33 of Fig. 3. A hub 69 of insulating 'material is affixed to the shaft 61 and has a wiper arm keyed to it for cooperating with the resistor element 338.

The sleeve 41 of the control member has fast upon it a cam 68b for engaging and thrusting downward a thrust rod 680 which passes through the stationary hollow shaft 46 and down into the stationary casing 42. A rack 68d affixed to the lower end of the rod 680 is provided at its lower end with a cap 68f which bears against a compression coil spring 68g, the spring serving to thrust the rack and rod upward and maintain the upper end of the rod 680 in engagement with the cam 68b. The rack 68d drives a pinion 68h fast on a shaft 68z'. The shaft 681' extends through a stationary casing 68k within which there is supported a resistor 66 corresponding to the resistor 6 of Fig. 3. A hub 6811. of insulating material is affixed to the shaft 68k and has a wiper arm 36e keyed to it for cooperating with resistor element 6e, Movement of the control member in either direction from the elevation neutral attitude causes an increase of the resistance included in the generator galvanometer circuit of the elevation drive as explained in connection with Fig. 3.

The electrical connections are not fully illustrated in detail in Figs. 1 and 2, because they have been illustrated and described in Fig. 3, and because their inclusion in Figs. 1 and 2 would tend to obscure the disclosure of the mechanical parts. It will be understood, however, that the wiper arm 31c carried by the shaft 6'! corresponds to the slide contact 31 of Fig. 3, that the wiper arm 36c corresponds to slide contact 36 of Fig. 3, and that each part to which a reference numeralof Fig. 3 has been applied with a or e added corresponds to the parts bearing the same numeral in Fig. 3, and is electrically connected in the manner illustrated by Fig. 3. The appropriate conductors for the elevation drive are carried from casing 42 to the elevation motor generator Ie through a conduit 68p.

The output shaft l2e of the motor-generator Ie has affixed to it a pinion I3 which meshes with an elevation segment I4, fast on a horizontal shaft I5. The shaft I5 is mounted forrocking movement in fixed bearings (not shown) 7 of the'turreti Two machine guns I6 are afilxed'to the shaft 15, and are operated in elevation by rocking movements imparted-to theshaft. The guns, obviously, are raised by rotation of the motor shaft 'I2e in one direction and are depressed by rotation of the motor shaft I26 in the opposite direction.

The mechanism for operating the turret about its vertical axis to operate the guns in azimuth is in general similar to that which has been described for operating the guns in elevation.

The control box 45 may be turned about its vertical axis (coincident with the axis of the shaft 46) by operation of the control handles 48. The shaft 46 does not participate in this movement, but is fixedly mounted in the stationary casing 42 to extend up into the control box 45. Rotation of the control box does, however, carry with the control box about the axis of shaft 46a vertical shaft 11, a galvanometer 29a, and a galvanometer shaft 35a.

Shaft 46 has affixed to it a gear segment 19,

which meshes with a gear segment fast on shaft TI. The segment 88 is connected through a coil spring 8| with a contact arm I4a fast on the galvano meter shaft 35a. The arm He carries contact blades I5a and I8a which extend between arms of a yoke-like contact carrying block 82. The block 82 is affixed to the partition wall 65 of the control box 45. The block 82 carries contacts l6a and I9a. for cooperation, respectively, with contacts carried by the blades [5a and ISa. A vertical shaft 83 carried by the stationary casing 42 has aflixed to the upper end thereof a pinion 84 which meshes with a gear 85 affixed to the control box 45. The shaft 83 extends axially through a resistor casing I8, the casing I8 being stationarily mounted in the stationary casing 42. The gear 85 is coaxial with the shaft 46. Rotation of the gear 85 with the control box 45 causes the pinion 84 and the shaft 83 upon which it is mounted to rotate.

The casing I8 includes a resistor 33a corresponding to resistor 33 of Fig. 3, and the shaft 83 has fixed upon it, but insulated from it, a wiper arm like the wiper arm 31c, the function of these parts being the same in the azimuth drive as that of the corresponding parts in the elevation drive. The shaft 83 also extends through a casing 18b which includes a resistor 6a, and the shaft 83 has fixed upon it, but insulated from it, a wiper arm like the wiper arm 31a, the function of these parts being that described in connection with the parts 31 and 33 of Fig. 3.

As in the case of the segment 49, provision is made of means tending to restore and to maintain the control box 45 in its neutral position. A coil spring 86 surrounds a flange on gear 85, The ends of the spring 86 are turned outward to form arms 88 and 89 which lie at opposite sides of a pair of pins 90, the pins being affixed to the casing 42 and extending upwardly therefrom. A pin 3| affixed to the gear 85 extends downwardly from the gear between the arms 88 and 89. The pin 9| carries one or the other of the arms 88, 89 around in front of it as the control box is rotated away from neutral while the other of the arms 88, 89 is restrained from following through engagement with the stationary pins 90. The operation is exactly the sam in principle as that described for the corresponding mechanism in connection with the gear segment 49.

The appropriate conductors for the azimuth drive are carried from casing 42 to the azimuth motor-generator Ia through a conduit 93. The motor-generator la is mounted upon and affixed to the turret. The output shaft I2a of the motorgenerator Ia has affixed to it a pinion 94 which meshes with the internal teeth of the stationary ring gear 4|. Operation of the motor-generator shaft is effective, therefore, to drive the turret about its vertical axis in one direction or the other relative to the stationary ring gear 4|, the direction of rotation depending upon the direction in which the motor shaft l2a is driven.

In the form of the invention diagrammatically disclosed in Fig. 4, a double shunt D. C. motor MI is connected through line conductors I42 and I43 with a source of direct current. The current flows from conductor I42 through a conductor I44 to the armature I45 of the motor and returns thence through a conductor I46 and a variable resistance I4! to conductor I43. Current may also flow through either of two opposed field windings I48 and I43 which are connected in parallel with one another. One path is from I42 through conductors I58 and I5l, winding I48, conductor I52, contacts I53 and I54, and a return conductor I55 to conductor I43. The other path. is from I42 through conductors I and I56, winding I48, conductor I51, contacts I50 and I53, and return conductor I to conductor I43. The field circuits described are normally open, and are closed alter natively to cause the motor to be driven selectively in one direction or the other.

The contacts I53 and I58 are carried on a manual control member I60, which is mounted for pivotal movement coaxially with the shaft IOI of a galvanometer I62. The motor I4I drives a D. C, generator I63 which is connected to the galvanometer I62 through a conductor I64, on the one hand, and through a conductor I65, a slide contact I65 carried by an arm I61 of control member I60, a center connected resistor I68, like resistor 33 of Fig. 3, and a conductor I69, on the other hand.

The contacts I54 and I59 are mounted on an arm I10 which is fast on the galvanometer shaft I6I. A coil spring I1I which surrounds the galvanometer shaft I6I and which is connected at one end to the arm I10 and at the other to a stationary pin I12 tends to maintain the arm I10 in the normal or neutral position illustrated in Fig. 4 when no electrical potential is applied to the galvanometer.

In the normal or neutral position, neither of the windings I48 and I49 is energized, and the motor remains idle. When the manual control member I is swung counter-clockwise, contact I58 is first carried into engagement with contact I59, and further counter-clockwise movement of the control member I60 swings the arm I10 in a counter-clockwise direction against a progressively increasing stress of the spring I1I. When the control member I60 is moved from neutral in a clockwise direction, contact I53 is first carried into engagement with contact I54, and further movement of the control member in a clockwise direction moves the arm I10 in a clockwise direction against a progressively increasing stress of the spring I1I,

The immediate effect of engagement of contacts I58 and I59 is to set the motor .into operation in one direction, while the immediate effect of engagement of the contacts, I53 and I54 is to set the motor into operation in the opposite direction. In the former case the tendency of the stress of spring I1I is to presscontact I 59 clockwise against contact I50, but thetendency of the generated voltage is to apply acounter-clockwise torque to arm I10 which tends to. separate the contacts. When the electrically developed torque is sufficient to overcome the spring torque, contact I59 is moved out of engagement with contact. I 50 and the motor immediately begins to lose speed. This causes the generated voltage to drop and enables the spring IN to restore engagement of contacts I59 and I50, so that the motor immediately starts to gain speed again. Since the stress of the spring depends upon the position to which the control member I60 has been moved, there will be a definite motorspeed corresponding to any selected position of the manual control member I60. When the manual control member is moved counter-clockwise to engage contacts I53 and I54, the operation is precisely the same in principle as that which has just, been described, the only difference being that operation of the motor is in the opposite direction.

A ballast resistance I41 is provided in circuit with the armature I45 which is automatically and progressively varied in accordance with load conditions, to providea relatively high resistancein 12 series with the armature under no.load conditions and a relatively low resistance inqseries with the armature under full load conditions.

Connection between. the resistance I41 and line conductor I43 is effected through a slide contact In whichis mountedon. an arm- I14 carried by shaft I15- of a reversible servo-motor I123. The servo-motor: I16is a double shunt D. C. motor. Thearmature I11 of. motor I16 is connected to conductor I42 through conductors I10 and I19, and to conductorI43through conductors I00 and I55; Conductor, I18 is connected through one field winding I8I with a contact I82, and through the other field winding I83 with a contact I04. A

r switch I connected through a conductor I06 to conductor I55 is adapted to engage either contact I82 ci -contact I84, sothat the motor I16 may be connected to: drive thearm I14 in one direction or the other. The conductor. I55 has interposed initarelay I81. When the relay I81 is energized it draws the switch I85 toward the left into engagementwithcontact I 82. When the relay I 81 is notenergized,v a spring I88-draws the switch I85.,t0 the right and into engagement with contactl04..

The relay I81 is designed to overcome the tension ofthe spring I88 only when appreciable current fiows.

Fig-8.shows the speed-timecurves of the power motor,v curve-a indicating-power motor speed at substantiallyno load condition and curve b power motor speed at.ful1, load condition. It will be noted, by comparing thecurves, that both curves areof saw tooth shape and of equal amplitude. but that the periods of acceleration under no-load conditions arerelatively shorter than the periods of acceleration under load conditions, and further, that the periods of deceleration at no-load condition are relatively longer than the periods of deceleration under load. In effect, the speedtime curve contour is determinedby power motor load condition.

Whenthe power motor is first set into operation-the'eifective resistance of I41 may be of maximum. value; but switch I05 immediately closes oncontact I82.and causes the resistance of I41 .to be continuously reduced until the speed hasbeen attained for which control member I60 has been set. Then, when the effective field circuit of motor MI is opened, switch I85 leaves I 82 and engages I04, causing the resistance of I41 to be increased. So long as the setting of IGOremains unchanged, the switch I85 oscillates to engage I84'and I82 in alternation, according to whether the circuit of the effective field winding of MI is open or closed.

Under no-load conditions as shown in Fig 8, the contact arm I 85 is held against contact I82 by the relay I81 approximately one-third as long as it is-held against contact I84 by the spring I80. This causes the effective resistance of I41 to be progressively increased, and as the resistance is increased, the periods of increase and decrease gradually tend to become equalized. Under no-load conditions, however, equalization is not attained, and the eifective resistance of I41 is progressively increased until a maximum value for resistance I41 is reached, whereupon the arm I14 contacts a mechanical stop I09. No injury will result to the servo-motor, since it is designed to operate in a stalled condition.

Under maximum load conditions, the servomotor operates as described above, but the cumulative operations act to step down the resistance. Again the periods of increase and decrease gradually tend to become equalized in responseto theqprogressive adjustment of the effective resistance of I41, but equalization is not attained, and the effective resistance is adjusted to a predetermined minimum value, whereupon the arm H4 is again arrested by engagement with a stop I90.

At intermediate constant loads the servo-motor operates to adjust the resistance value until the speed-time curve becomes symmetrical, whereupon the servo-motor remains in equilibrium; i. e., produces no net increase or decrease of resistance. It should be noted that the described operations occur at a frequency high enough to insure smooth and stable operation of the system.

The described electric drive of Fig. 4 may be employed in the azimuth drive and in the elevation drive of Figs 1 and 2, and the two drives may be operated by the common control means described in Figs 1 and 2.

In the form of the invention disclosed in Fig. 5, centrifugal means, instead of the generator-galvanometer combination of Figs. 3 and 4, are utilized. A double shunt D. C. motor MI is employed. A D. C. source, as battery 202, is connected to the motor armature 203 through conductors 204 and 205, a wiping contact 206, a ring resistor 201, and a conductor 208. The return path from the armature 203 to the battery 202 is through conductors 209 and 210. Opposed field windings 2H and 212 are adapted to be connected alternatively to the current source 202.

Provision is made of means for yieldingly closing the circuits of the field windings 2H and NZ to produce rotation of "the motor. armature and shaft in one direction or the other as desired. Speed responsive means including fly-weight governors are provided for interrupting the effective .circuit when a predetermined speed has been attained, characteristic of the position to which a manual control member 2l3 has been moved. Thecontrol member 2 l3 operates the contact 206 in unison with itself.

The motor output shaft 214' drives a shaft 2l5 which, through one-way clutches I08 and I09, drive trains 216 and 211, respectively, the trains 2 l8 and 2I9 being connected to drive wheels 220 and HI which are mounted on stationary bearings 222 and 223. When the shaft 2M turns in one direction, it drives the train 2l8 and the wheel 220 at a speed proportional to its own speed, but the train 2l9 and the wheel 22l remain idle. When the shaft 2l4 is driven in the opposite direction, it drives the train H9 and the wheel 22I at a speed proportional to its own speed, but the train H8 and the wheel 220 remain idle.

The wheel 220 carries a plurality of bent conductive spring arms 224. Each arm has affixed to it intermediate its ends a fly-weight 225 and carries at its inner end a contact member 226. The arms 224 are mounted in insulated bushings 221 and are connected electrically to a ring conductor 228 which is mounted upon, but insulated from, the wheel 220.

A conductivesleeve 229 formed with an end flange 230 is mounted in a bore of the bearing member 222 with the flange member 230 disposed at the outer or righthand side of the bearing member 222. A conductive disc 23! having a conductive stem 232 is mounted by means of an insulating sleeve 233 in fixed relation to the sleeve 229. The flange 230 and the disc 23l stand at opposite sidese of the contact members 226, and are spaced from the contact members 14 in the neutral condition of the parts as illustrated in Fig. 5.

The parts 224 to 233, inclusive, described in conection with the wheel 220 are duplicated in connection with the wheel 22l. Corresponding reference numerals have accordingly been applied to the corresponding parts with the subscript a added ineach instance, and the detailed description of them will not be repeated.

Springs 234 and 234a bear, respectively, against the discs HI and 23Ia, the former spring urging the stem 232 toward the left, and the latter urging the stem 232a toward the right. These stems bear against the manual control member 213 and the stresses of the two springs are balanced against one another through the manual control member in the normal or neutral position of the latter.

When the manual control member is swung in a clockwise direction away from the neutral position illustrated in Fig., 5, the stem 232 and the sleeves 233 and 229 are moved as a unit toward the right. The flange 230 first engages the con,- tacts 226 and then moves them toward the right, putting the spring arms 224 under stress.

. Engagement of the flange 230 with the contacts 226 closes the circuit of field winding 2. This path .includes the conductor 204, a conductor 23", field winding 2| l, conductors 236 and 231, sleeve 229, flange 230, contacts 226, arms 224, ring conductor 228, and conductors 238 and 2). This causes the motor shaft 2 to be driven through the action of field winding! in the direction to drivewheel 220.

The motor gains speed until the centrifugal forces exerted by the fly-weights 225 is sufficient to carry the contacts 226 outward away from engagement with the flange 230 to open the circuit of field winding 2. The motor shaft 2M and the wheel 220 thereupon lose speed until the stress exerted upon the arms 224 by the flyweights 225 is not greater than the stress imposed upon the arms 224 by the displacement of the sleeve 229 from its normal position. As soon as this occurs the contacts 226 reengage the flange 230 and the circuit for the field winding 2H is again established.

For the reason pointed out in connection with Fig. 4, the armature circuit of the motor is desirablymade to include a ring resistor 201 of suitable characteristics to assure slowing down of the motor as soon as engagement between the contacts 226 and the flange 230 is broken and to assure speeding up of the motor as soon as such engagement is reestablished.

Should the conditions be such that the motor does instantaneously speed up, however, at the breaking of contact, the contacts 226 will be carried not merely away from flange 230 but into engagement with the disc 23l and will thereby establish a circuit through the field winding 2l2 :to assure an immediate slowing down of the motor.

This circuit is through the conductor 204, a conductor 239, the Winding 2l2, conductors 240 and 24 I stem 232, disc 23f, contacts 226, arms 224,

ring conductor 228, and conductors 238 and M0.

The speed at which the motor operates depends upon the position to which the control member 2 I 3 has been moved, since the initial stress of the spring arms 224 which must be exceeded in order -to move the contacts 226 out of engagement with the flange 23l is determined by the position of the control member 2 l3. In operation, the mak- "ing and breaking of engagement between contacts 226and flange 23l occurs with such rapidity agcbdsaa that a substantially constant speed of the motor results.

When the control member 2|3 is displaced counter-clockwise from the neutral position, the normal circuit of field winding H2 is closed through a path which includes conductors 204 and 239, winding 2l2, conductors 240 and 242, sleeve 229a, contacts 226a, arms 224a, ring conductor 228a, and conductors 243 .and 2). This causes the motor shaft 2 to be turned in the direction opposite to that previously described, and causes the wheel 22l to be driven. The operation with reference to the wheel 2H and the parts associated therewith is in all respects the same as that described for. the wheel 220 and the parts associated with the latter for theopposite direction of rotation. Should the contacts 226a engage the disc 231a, field winding 2| I' will be momentarily energized through a circuit which includes conductors 2M and 235, winding 2, conductors 236 and 244, stem 232a, disc 231a, contacts 226a, arms 224a, ring conductor 228a, and conductors 243 and H0.

The described drive may be used in the azimuth and elevation drives of Figs. 1 and 2.

The principles of the invention may be practically and advantageously applied to an alternating current electric drive as well as to a direct current electric drive. In Fig. 6 disclosure is made of a practical and advantageous embodiment of the invention adapted to be operated from a suitable A. C. source. The embodiment chosen for illustration is generally similar to the embodiment of Fig. 4. The same reference characters applied in Fig. 4 have, therefore, been applied to corresponding parts in Fig. 6 with the subscript a added in each instance, and the description will be confined substantially to those parts which are necessarily different in Fig. 6 from Fig. 4 and to those parts which are added.

The motor Illa is supplied with alternating current from a suitable alternating current source through line conductors l42a and 3a. In the main, however, the motor Mia may be connected and controlled in the same manner as the motor M l Since the generator I634: and the galvanometer 182a have no electrical connections save to one another, the generator l63a may be a D. C. enerator, the same as the generator I63, and

the galvanometer I62a maybe the same as the r galvanometer I62.

In the development of conventional A. C. motors in order to secure a high power factor and in the interest of economical operation and design, armature reactance (Xa in the vector diagram of Fig. 8) is kept to a minimum. These motors, however, are never'required to run under open field conditions, and consequently no dangerously high current surge through the armature can occur.

When used with a control system of the type described, however, in which opening of the field circuits is a prime factor in securing speed regulation, it is imperative that current flow in the armature be restricted to safe limits in the armature, and, therefore, provisions for compensation corresponding to the series armature resistance of the D. C. motor must also be used with the A; C. motor. The compensation, in an A. C. system takes the form of regulated armature inductive reactance and regulated field reactance either inductive or capacitive, or combinations of both. insome designs.

The armature'of anyA. C. motor has some inherent inductance. If the value of this inductance, determined. by other factors in the design, is not sufficient, it may be augmented by additional armature inductance either in the form of a reversed compensating winding in the armature or, by a choke coil 3M exterior of the motor casing and in series with the armature as shown in Fig. 6.

In the event that the armature reactance is already too great in the particular motor design being considered, it may be reduced to the correct value by means of a compensating winding connected in conventional fashion, but of such value as to compensate only partially for the armature reactance to achieve the object outlined above. In most designs, however, it is likely that the armature reaotance will need to be increased rather than reduced.

The value of the inductance to be included in the armature circuitde-pends upon several factors, namely;

(a) Field. strength, which should be weak, in order to obtain as high a power factor as possible. and further to allow a light weight, high speed design.

(1)) Total armature reactance-including both the inherent reactance of the armature and any additional reactance inserted in the circuit. It must be great enough to limit the current flow to a safe value when the field is opened.

(0) Phase angle between the current in the armature and the field. This angle varies with internal resistance, equivalent load resistance and reactance in the armature, and with the resistance and reactance of the field. The phase angle should he as small as possible for all conditions of load, favoring the full load condition in most cases. It may be adjusted by changing the armature inductance, or (as is most likely to be the case) if the value of the armature in ductance is already fixed by condition (1)) above, varying the field reactance.

The field reactance may be decreased by adding capacitance as illustrated by the condenser 30! whichis inductively coupled to the conductor a of Fig. 6. This condenser could be inserted primarily in the field circuit but has preferably inductively coupled in by means of a transformer 3B3 as shown in Fig. 6. Use of a coupling transformer 303 as shown in Fig. 6 enables smaller condensers to be usedin cases where the required series capacitance is verylarge, as the equivalent capacitance varies with the square of the transformer turns ratio.

The field reactance may be increased, if necessary, by adding series inductance.

Referring to the vector diagram of Fig. 9, the symbol employed have the following meanings:

Zr:field impedance Za=armature impedance Xr=field reactance Xa=armature reactance RFfield resistance Ra=armature resistance (internal) lipphase angles, field 0a=phase angle, armature Ri -equivalent resistance of load a phase angle between armature and field eflux in field V=line volts Ia=armature current K=constant n revolutions per second Tqorque developed P-output power The following relationships prevail, and must be taken into account I The angles Br and a should, as nearly as possible, approach equality under full load, and yet still be not too far apart at standstill. That is, a. should be as nearly zero as possible at full load, consistent with sufiicient torque when the rotor is locked. Since the current will be higher with the rotor locked, some deviation of 0: from 95. can be permitted in this condition.

R: will be constant for any given motor and j X: will have a given value which may be varied by means of compensation of the condenser transformer type shown in Fig. 6. These factors establish Zr.

Ra is negligible, in a practical design, but R1 will vary directly with load. Some Xa will be inherent with the armature, and may be supplemented by reversed, compensating windings or a choke coil 30I as shown in Fig. 6. These factors establish Za. I

The form of the invention disclosed in Fig. 6 may be advantageously used in the azimuth drive and in the elevation drive of Figs. 1' and 2.

In the form of the invention disclosed in Fig. 7, the power motor and the speed responsive control means therefor may be the same as the corresponding parts of the mechanism disclosed in Fig. 4. The same reference numerals employed in Fig. 4 have accordingly been applied to the corresponding parts in Fig. 7, with the subscript b added in each instance, and these parts will not be further described in detail.

Current fiow through the armature of motor I4Ib is automatically limited to safe values while I making the maximum power available under high speed, full load conditions by interposing the armature of an auxiliary motor 40I between conductors M61) and I431; in series with the armature of motor I4Ib.

The motor 40| is a shunt motor having twoopposed field windings 402 and 403. When the line switch is closed, current flows continuously through winding 402. The path is from I42b through a conductor ,404 which includes a fixed resistor 405, winding 402, and conductor 406 to I43b. Winding 403 is open circuited when the motor I4Ib is not running, but is rendered active whenever either field winding of motor I4Ib is energized. The connection through winding 403 is from 404 through conductor 401, winding 403, conductor 408, a switch arm 40 9, contact M0, and a conductor 4 to I43b. Switch arm 409 is normally held open by a spring 4| 2, but, by virtue of relay I8'Ib, is closed upon contact 4I0 when the control member I601) is operated to close the circuit of either of the field windings I481), I491) of the power motor I4Ib.

The output power of motor 40I is dissipated through any suitable brake. As illustrated, the armature shaft 4 I 3 carries a rotor 4 I4 upon which friction shoes 4I5 are pivotally mounted. The shoes 4I5 cooperate with a stationary friction drum 4I6.

With the system energized and the control member I60b in the neutralposition, only the winding 402 of motor 40I will be energized. Motor 40I will, therefore, run at its maximum speed. Thecounter-electromotive'force in the armature 1 circuit of the motor 40I is proportional to speed, and may be considered the equivalent of resistance opposing current fiow through the armature of motor 40I and through the series connected armature of motor I4Ib.

When thecontrolmember 'I60b is operated to energize one or the other of the field windings I 48b, I49b of motor I4Ib, and thereby to set the motor I4Ib into operation, initial current flow through the armature of motor I 4Ib is held to safe limits by the relatively high counterelectromotive force of 40I.

Since the fields 402 and 403 are in opposed relation to one another, and since the field 403 is energized whenever either field of motor I4Ib is energized, one consequence of operating control member I601) to set motor I4Ib into operation is to effect a slowing down of the motor 40I. Thus as motor I4Ib gains speed,'motor40l loses speed, and as the counter-electromotive force of motor I4Ib increases, the counter-electromotive force of motor 40I. diminishes. More power is progressively made available for motor I4 ID as motor 40I slows down, but without liability of burning'out the armature of motor I 4Ib.

Field winding 403 and its circuit may be caused to, bearany desired .relationto field winding 402 and the circuit of 402 suitable for securing the character of operation desired. For reasons pointed out in connection with Fig. 4, however, it is not desirable that the counter-electromotive force of motor I4I shall exceed one-half the line voltage. Hence, it is desirable that the counterelectromotive force of motor 40I, plus any I. R. drop ofthe common armature circuit of the two motors, shall never be less than one-half of the line voltage.

If the circuit of 403 is made exactly equal in all respects with the circuit of 402, and if both circuits were permitted to be energized for a protracted period, the winding 403 would cancel out the winding 402, and the motor 40I would be brought to rest. This condition is not desired, nor will it occur in the illustrative apparatus, for 403 is energized only intermittently while 402 is energized continuously. Under stabilized operating conditions of motor I4I the active field winding of that motor is energized and deenergized alternately for equal periods, and hence the winding 403 is likewise energized and deenergized alternately :fo'requal periods.- Since the winding 402 under these conditions is substantially balanced or canceled out half the time and is substantially unopposed by 403 half the time, the motor 40I under the conditions described will run atsubstantially one-half the maximum speed which it attains when the motor MI!) is idle. The counter-electromotive force of motor 40I. therefore, varies between a maximum value sufiicient to protect the armature of motor I5Ib when the latter is idle, and a minimum value substantially equal to one-half the maximum. As already noted, .however, this speed relationship can be varied by varying the characteristics of the circults of windings 402 and 403 relative to one another, if required or permitted by operating requirements or by characteristics of design of the other parts; More particularly, it will be noted that the motor 40I may be allowed to drop to a lesser speed if a fixed resistance of substantial value is interposed in the common circuit of the armatures of motors MI!) and 40I.

The mechanism of Fig. 7 may be utilized to advantage in boththe elevation drive and the azimuth drive of Figs. 1 and 2.

The form of the invention illustrated in Fig. is adapted for direct current operation, and is general'y similar to the form of the invention dise closed in Fig. 4. The reference numerals employed in connection with Fig. 4 have accordingly been applied to the corresponding parts, and no further detailed description will be given of these Parts.

The means for regulating and adjusting the resistance in circuit with the armature of the motor in Fig. 10 is different from the corresponding means disclosed in connection with Fig. 4. Conductor I460 is connected to fixed resistances 50I and 502. Resistance 50I is constantly connected in series with the armature of motor I4Ic, but resistance 502 which is arranged in parallel with MI is cut in and out in response to operation of control member I500. Resistance 50l is connected through conductors 503, 504 and 505 with line conductor I430. Resistance 502 is adapted to be connected with line conductor I430 through a conductor 506, switch contact 501, switch member 5013, switch contact 509 and conductors 504 and 505.

In the normal or at rest condition of the motor I4 Ic resistance 502 is open circuited, switch member 500 being held away from contacts 501 and 509 by means of a spring 5I0, and being adapted to be closed by a relay 5| I when the control member I800 is in a position corresponding substantially to one-half the maximum speed for which the control member I600 may be set. For energizing relay 5, line conductor I420 is connected through a conductor 5I2 with armature I510 of the manual control member I600. Arma-. ture I610 carries a pair of contacts 5I3 and 5I4 for engaging, respectively, contacts 5I5 and 5l6. The normal spacing of contact 5I5 from the contact 5I3 is such that 5I3 and 5I5 will become engaged after a predetermined movement of the.

control member I600 from the neutral position as already referred to. After such engagement has been established, the control member is still free to continue its movement, the contact 5I5 being mounted so that it may be yieldingly forced back by the contact 5I3 but will be resiliently returned to its normal position when the pressure of con tact 5I3 against it is withdrawn. The relation-v ship of contact 5I5 to contact 5I4 is the same as that of contact 5I5 to 5l3.

When engagement is established either between H3 and 5I5 or between 5I4 and 5I6, current flows from armature I510 through the engaged pair of contacts, and thence through either of two parallel conductors 5I'1, 5I8 to a conductor 5I9. From conductor 5l9 the path continues through the winding of relay 5 and thence through a conductor 520 andconductor 505 to line conductor I430.

So long as the control member I600 has not been displaced from neutral far enough to engage 5I3 with 5I5 or 5I4 with 5I6, resistance 502 is not connected in circuit with the armature of motor I4I0. As soon as engagement of either pair of contacts is effected, however, relay 5 is energized and switch member 508 is caused to close upon contacts 501 and 509 for connecting resistance 502 in series with the armature of motor I4Ic, but in parallel with resistance 5 0I. This brings about a lowering of the resistance in series with the armature of motor I4Ic, so that more power is made available for driving the motor in the higher range of speeds. The parallel arrangement of the resistances 50 l and 502 is an advantageous one for the reason that the resistance of the armature circuit is reduced to enable more current to flow by adding an additional resistance path rather than by cutting resistance out of the circuit. Resistance 502 is thus caused to assist resistance 50I in absorbing and dissipating the heat developed by the flowing current.

The disclosed mechanism provides two steps of resistance in series with the armature of motor I4Ic. Additional steps may be provided, however, by providing additional resistance elements in parallel with SDI and 502 together with means for switching in the resistances successively at successive points in the operation of the manual control member. The two step arrangement, however, has been found to work well in practice and will generally meet all practical requirements.

The mechanism diagrammatically illustrated in Fig. 10 may be advantageously used in the elevation drive and in the azimuth drive of Figs. 1 and 2.

While the point has been stressed that the various forms of electric drive illustrated may be advantageously employed in the azimuth and elevation drives of Figs. 1 and 2, it should be observed that such use is referred to by way of illustration and not of limitation. Any one of the electric drives disclosed may be employed in any situation in which a variable output speed under the control of an operator is wanted.

We have described what we believe to be the best embodiments of our invention. We do not wish, however, to be confined to the embodiments shown, but what we desire to cover by Letters Patent is set forth in the appended claims.

What is claimed is:

1. A reversible, adjustable speed, electric drive comprising, in combination, a shunt wound motor having an armature and a pair of opposed field windings, circuit means for connecting the armature in circuit with a source of current supply, circuit means for rendering the field windings alternatively effective that one to drive the motor in one direction and the other to drive the motor in the opposite direction, comprising a first pair of contacts for establishing a circuit including the first of said field windings but not the second, and a second pair of contacts for establishing a circuit including the second of said field windings but not the first, each pair of contacts including a manually settable contact and a cooperative speed responsive contact, a manual control member operable selectively in opposite directions from a neutral position throughout a prescribed range to cause one or the other pair of contacts to become engaged, means for causing the engaged contacts to be pressed together with progressively increased force as the extent of departure of the manual control member from neutral is increased. and means operated by the motor for shifting the engaged speed responsive contact out of engagement with the cooperative manually settable contact against the force tending to hold them in engagement, when the motor speed exceeds a value characteristic of the position to which the manual control member has been moved, said means operated by the motor for shifting the speed responsive contacts out of engagement with the manually settable contacts comprising a generator driven by the motor, and a galvanometer operated by the generator and including a galvanometer output arm for shifting the speed responsive contacts.

2, A reversible, adjustable speed, electric drive comprising, in combination, a shunt wound motor having an armature and a pair of opposed field windings, circuit means for connecting the armature in circuit with a source of current supply, circuit means for rendering the field windings alternatively effective the one to drive the motor in one direction and the other to drive the motor in the opposite direction, comprising a first pair of contacts for establishing a circuit including the first of said field windings but not the second, and a second pair of contacts for establishing a circuit including the second of said field windings but not the first, each pair of contacts including a manually settable contact and a cooperative speed responsive contact, a manual control member operable selectively in opposite directions from a neutral position throughout a prescribed range to cause one or the other pair of contacts to become engaged, means for causing the engaged contacts to be pressed together with progressively increased force as the extent of departure of the manual control member from neutral is increased, and means operated by the motor for shifting the engaged speed responsive contact out ofengagement with the cooperative manually settable contact against the force tending to hold them in engagement, when the motor speed exceeds a value characteristic of the osition to which the manual control member has been moved, said means operated by the motor for shifting the speed responsive contacts out of engagement with the manually settable contacts comprising a generator driven by the motor in harmony with the speed and direction of the latter, and a galvanometer operated by the generator including an output arm for operating the speed responsive contacts in one direction or the other according to the direction of rotation of the motor and with a force which varies with the motor speed.

3. A reversible, adjustable speed, electric drive comprising, in combination, a shunt wound motor having an armature and a pair of opposed field windings, circuit means'ior connecting the armature in circuit with a source of current supply, circuit means for rendering the field windings alternatively effective the one to drive the motor in one direction and the other to drive the motor in the opposite direction, comprising a first pair of contacts for establishing a circuit including the first of said field windings but not the second, and a second pair of contacts for establishing a circuit including the second of said field windings but not the first, each pair of contacts including a manually settable contact and a cooperative speed responsive contact, a manual control member operable selectively in opposite directions from a neutral position throughout a prescribed range to cause one or the other pair of contacts to become engaged, means for causing the engaged contacts to be pressed together with progressively increased force as the extent of departure of the manual control member from neutral is" increased, and means operated by the motor for shifting the engaged speed responsive contact out of engagement with the cooperative manually settable contact against the force tending to hold them in engagement, when the motor speed exceeds a value characteristic of the position to which the manual control member has been moved, said means operated by the motor for shifting the speed responsive contacts out of engagement with the manually settable contacts comprising a generator driven by the motor in harmony with the speed and direction of the latter, and a galvanometer operated by the generator including an output arm for operating the speed responsive contacts in one direction or the other according to the direction of rotation of the motor and with a force which varies with the motor speed, and said means further including a center connected rheostat in series with the generator and galvanometer and a sliding contact operated by the manual control member away from the center point of the rheostat upon move ment of the manual control member away from the normal neutral position thereof, so that the effective resistance of said rheostat is caused to increase in accordance with the extent of departure of the manual control member from new tral in either direction.

4. An electric drive comprising, in combination, a shunt wound motor which includes an armature and a field winding, circuit means for connecting the armature in circuit with a source of current supply, circuit means comprising a pair of cooperative contacts for rendering the field winding effective and ineffective to drive the motor, a manual control member operable away from an at rest position for setting the first contact in engagement with the second, means for causing the contacts to be pressed together with progressively increased force as the extent of departure of the manual control member from the at rest position is increased, and speed responsive means operated by the motor for disengaging said contacts and maintaining them disengaged against the force tending to hold them engaged whenever the motor speed exceeds a speed characteristic of the position to which the manual control member has been moved, a plurality of fixed resistance elements connected in series with the motor armature but in parallel with one another, one of said resistance elements being constantly connected in a closed circuit path with the armature and a source of electrical energy, and another being normally open circuited, and means responsive to the manual control member for closing the circuit of the latter resistance element when the manual control member has been moved away from the at rest position thereof to a predetermined extent.

5. A reversible adjustable speed electric drive comprising, in combination, a reversible motor, circuit means for supplying driving energy to drive the motor selectively in one direction or the other, comprising a first pair of contacts for establishing a circuit to drive the motor in one direction, and a second pair of contacts for establishing a circuit to drive the motor in the opposite direction, each pair of contacts including a manually settable contact and a cooperative speed responsive contact, a manual control member operable selectively in opposite directions from a neutral position throughout a prescribed range to cause one or the other pair of contacts to become engaged, means for causing the engaged contacts to be pressed together with progressively increased force as the extent of departure of the manual control member from neutral is increased, and means operated by the motor for shifting the engaged speed responsive contact out of engagement with the cooperative manually settable contact against the force tending to hold them in engagement, when the motor speed exceeds a value characteristic of the position to which the manual control member has been moved, said means operated by the motor for shifting the speed responsive contacts out of engagement with the manually settable contacts comprising a gen- 23 24 erator driven by the motor, and a galvanometer REFERENCES CITED operated by the generator and including The following references are of record in the vanometer output arm for shifting the speed file of this patent, responsive contacts.

CENTRAL HANOVER BANK AND 5 UNITED STATES PATENTS TRUST COMPANY Number Name Date Corn- Emecutor of the Estate of Peter J.McLaren, 2,332,611 Spencer Oct 26, 1943 Deceased.

By E. E. BREMNER,

Asst. Treasurer. 10

JOHN A. VAUGHAN. MACON FRY.

Certificate of Correction Patent No. 2,456,522. December 14, 1948.

PETER J. McLAREN, DECEASED, BY CENTRAL HANOVER BANK AND TRUST COMPANY, EXECUTOR, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 20, line 43, claim 1, for the Word that read the;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 12th day of April, A. D. 1949.

THOMAS F. MURPHY,

Assistant O'ommissz'oner of Patents. 

